A conventional load drive circuit, which performs the switching control of an electric load such as a motor, adopts a noise filter for reducing noise that occurs at the switching of the load. In such a noise filter, however, a coil acts as a resistor, so a supply voltage to be fed to the load is reduced.
In this regard, a method for lowering the loss of the noise filter has been proposed in JP 2001-23809A and JP 2001-23811A. Specifically, powder of Fe—Ni-based soft magnetic alloy being a composite magnetic substance of high permeability is employed as a metallic composite magnetic material of high performance for the noise filter, and a compressed powder magnetic core made by the compression molding of the powder is used.
With the method in JP 2001-23809A, the loss of the noise filter is lowered by enhancing the material characteristics of the magnetic material employed for the noise filter. However, the configuration of the noise filter employing the coil is the same as that of the conventional noise filter, and hence the resistance of the coil cannot be nullified completely. Accordingly the supply voltage to be fed to the load is reduced by the coil in the noise filter.